1. Field of the Invention
The invention relates to a digital scan converter for a pulse radar apparatus provided with: a random-access memory, each cell of which containing brightness data; a circuit connected to the memory for reading out the brightness data and for presenting corresponding video signals on a raster scan display at positions unit for supplying persistence data and address information to process the persistence data; switching means for passing either radar video signals or the persistence data; and a logical unit for supplying, in response to the radar video signals and the persistence data, respectively, and to the brightness data stored in memory, new brightness data overwriting that stored in memory, whereby the memory positions are determined by an address conversion circuit which converts the radar video addresses and the persistence data addresses established in polar coordinates by the pulse radar apparatus and the control unit, respectively, into addresses expressed in Cartesian coordinates.
2. Description of the Prior Art
Such a digital scan converter is known from the U.S. Pat. No. 4,165,506. This converter contains a timing unit, which delivers brightness-reducing command signals at such fixed instants of time, that a persistence is obtained resembling that of a long-persistence phosphor on the display. The addresses pertaining to these command signals are generated in a pseudo-random sequence to effect a uniform reduction in brightness on the display. The present invention however has for its object to provide a digital scan converter, as set forth in the opening paragraph, attaining a persistence that resembles that of a PPI display, where the displayed radar scan shows a tangential persistence, i.e. a persistence proceeding in its direction of motion.